1. Field of the Invention
The present invention relates generally to an evaporative type cooling system for an internal combustion engine wherein liquid coolant is permitted to boil and the vapor used as a vehicle for removing heat therefrom, and more specifically to a simple and compact vapor manifold for such a system which attenuates excessive transmission of liquid coolant along with the coolant vapor between the engine coolant jacket and the radiator or condensor in which the coolant is condensed back to its liquid form.
2. Description of the Prior Art
In currently used "water cooled" internal combustion engines (liquid) is forcefully circulated by a water pump, through a cooling circuit including the engine coolant jacket and an air-cooled radiator. This type of system encounters the drawback that a large volume of water is required to be circulated between the radiator and the coolant jacket in order to remove the required amount of heat.
Further, due to the large mass of water inherently required, the warm-up characteristics of the engine are undesirably sluggish. For example, if the temperature difference between the inlet and discharge ports of the coolant jacket is 4 degrees, the amount of heat which 1 Kg of water may effectively remove from the engine under such conditions is 4 Kcal. Accordingly, in the case of an engine having an 1800 cc displacement (by way of example) is operated full throttle, the cooling system is required to remove approximately 4000 Kcal/h. In order to achieve this, a flow rate of 167 liter/min (viz., 4000-60.times.14) must be produced by the water pump. This of course undesirably consumes several horsepower.
FIG. 2 shows an arrangement disclosed in Japanese Patent Application Second Provisional Publication Sho. No. 57-57608. This arrangement has attempted to vaporize a liquid coolant and use the gaseous form thereof as a vehicle for removing heat from the engine. In this system the radiator 1 and the coolant jacket 2 are in constant and free communication via conduits 3, 4 whereby the coolant which condenses in the radiator 1 is returned to the coolant jacket 2 little by little under the influence of gravity.
This arrangement while eliminating the power consuming coolant circulation pump which plagues the above mentioned arrangement, has suffered from the drawbacks that the radiator, depending on its position with respect to the engine proper, tends to be at least partially filled with liquid coolant. This greatly reduces the dry surface area via which the gaseous coolant (for example steam) can effectively release its latent heat of vaporization and accordingly condense, and thus has lacked any notable improvement in cooling efficiency. Further, with this system in order to maintain the pressure within the coolant jacket and radiator at atmospheric level, a gas permeable water shedding filter 5 is arranged as shown, to permit the entry of air into and out of the system.
However, this filter permits gaseous coolant to readily escape from the system, inducing the need for frequent topping up of the coolant level. A further problem with this arrangement has come in that some of the air, which is sucked into the cooling system as the engine cools, tends to dissolve in the water, whereby upon start up of the engine, the dissolved air tends to come out of solution and forms small bubbles in the radiator which adhere to the walls thereof and form an insulating layer. The undissolved air also tends to collect in the upper section of the radiator and inhibit the convention-like circulation of the vapor from the cylinder block to the radiator. This of course further deteriorates the performance of the device.
European Patent Application Provisional Publication No. 0 059 423 published on Sept. 8, 1982 discloses another arrangement wherein, liquid coolant in the coolant jacket of the engine, is not forcefully circulated therein and permitted to absorb heat to the point of boiling. The gaseous coolant thus generated is adiabatically compressed in a compressor so as to raise the temperature and pressure thereof and thereafter introduced into a heat exchanger (radiator). After condensing, the coolant is temporarily stored in a reservoir and recycled back into the coolant jacket via a flow control valve.
This arrangement has suffered from the drawback that when the engine is stopped and cools down, the coolant vapor condenses and induces sub-atmospheric conditions which tend to induce air to leak into the system. This air tends to be forced by the compressor along with the gaseous coolant into the radiator.
Due to the difference in specific gravity, the above mentioned air tends to rise in the hot environment while the coolant which has condensed moves downwardly. The air, due to this inherent tendency to rise, tends to form pockets of air which cause a kind of "embolism" in the radiator and which badly impair the heat exchange ability thereof.
With this arrangement the provision of the compressor renders the control of the pressure prevailing in the cooling circuit for the purpose of varying the coolant boilding point with load and/or engine speed difficult.
U.S. Pat. No. 4,367,699 issued on Jan. 11, 1983 in the name of Evans (see FIG. 3 of the drawings) discloses an engine system wherein the coolant is boiled and the vapor used to remove heat from the engine. This arrangement features a separation tank 6 wherein gaseous and liquid coolant are initially separated. The liquid coolant is fed back to the cylinder block 7 under the influence of gravity while the relatively dry gaseous coolant (steam for example) is condensed in a fan cooled radiator 8.
The temperature of the radiator is controlled by selective energizations of the fan 9 which maintains a rate of condensation therein sufficient to provide a liquid seal at the bottom of the device. Condensate discharged from the radiator via the above mentioned liquid seal is collected in a small reservior-like arrangement 10 and pumped back up to the separation tank via a small constantly energized pump 11.
This arrangement, while providing an arrangement via which air can be initially purged to some degree from the system tends to, due to the nature of the arrangement which permits said initial non-condensible matter to be forced out of the system, suffers from rapid loss of coolant when operated at relatively high altitudes. Further, once the engine cools air is relatively freely admitted back into the system. The provision of the bulky separation tank 6 also renders engine layout difficult.
The rate of condensation in the condensor is controlled by a temperature sensor disposed on or in the condensor per se.
Japanese Patent Application First Provisional Publication No. sho. 56-32026 (see FIG. 4 of the drawings) discloses an arrangement wherein the structure defining the cylinder head and cylinder liners are covered in a porous layer of ceramic material 12 and wherein coolant is sprayed into the cylinder block from shower-like arrangements 13 located above the cylinder heads 14. The interior of the coolant jacket defined within the engine proper is essentially filled with gaseous coolant during engine operation at which time liquid coolant sprayed onto the ceramic layers 12.
However, this arrangement has proven totally unsatisfactory in that upon boiling of the liquid coolant absorbed into the ceramic layers, the vapor thus produced and which escapes toward and into the coolant jacket, inhibits the penetration of fresh liquid coolant into the layers and induces the situation wherein rapid overheat and thermal damage of the ceramic layers 12 and/or engine soon results. Further, this arrangement is of the closed circuit type and is plagued with air contamination and blockages in the radiator similar to the compressor equipped arrangement discussed above.
FIG. 7 shows in arrangement which is disclosed in U.S. Pat. No. 4,549,505 issued on Oct. 29, 1985 in the name of Hirano. The disclosure of this application is hereby incorporated by reference thereto. For convenience the same numerals as used in the above mentioned Patent are also used in FIG. 7.
This arrangement while solving the drawbacks encountered with the previously disclosed prior art has itself suffered from the drawbacks that when the engine is operated under high speed/load conditions, the boiling of the coolant in the coolant jacket 120 becomes so vigorous as to bump and froth to the degree that sufficient liquid coolant flows from the coolant jacket to the radiator 126 as to wet the interior of the latter mentioned device to the point of inhibiting the release of the latent heat of evaporation of the gaseous coolant. Viz., the liquid film on the wetted surfaces of the radiator act as an insulator which prevents the heat in the vapor from being readily released. This situation is highly undesirable in that the engine tends to be combusting large amounts of fuel per unit time at this time (ie. high speed/load operation) and thus induces the demand for a high radiator heat exchange efficiency.
FIGS. 8 and 9 show an arrangement disclosed in U.S. Pat. No. 4,499,866 issued on Feb. 19, 1985 in the name of Hirano which directed to overcomming the "boil-over" type problem discussed hereinabove. This arrangement includes a vapor manifold 232 which is mounted atop of a cylinder head which has a internal passage structure designed to limit the boiling froth which actually enters the manifold per se. The manifold 232 as shown, has a collector section 234 which is located vertically above the vapor discharge ports 216 formed in the cylinder head. With this, any liquid coolant which precipitates out of the vapor flow due to the numerous changes in flow direction which occur before the flow reaches the outlet 238 of the manifold, tends to drain back down into the coolant jacket partially quelling the upwardly moving coolant froth and foam.
However, as shown the overall height of the engine is increased by the provision of this type of manfifold and thus induces design problems when attempting the lower the bonnet line of an automotive vehicle wherein the engine is located in the forward section of the engine.
The content of the above mentioned United States Patent is hereby incorporated by reference thereto. For ease of comparison the numerals used in FIGS. 8 and 9 differ from those used in the corresponding drawings of the said patent only by the addition of the value of 200 to each. Viz., numeral 10 becomes 210 etc.